1. Field of the Invention
The present invention relates to organic strippers, cleaners and rinsing solutions used on microlithographic substrates and is particularly concerned with the improved removal of highly polar aromatic polymers and copolymers from the edge of substrate.
2. Background of the Prior Art
Single and/or multiple layers of microlithographic coatings including, for example, photoresist layers, planarization layers, anti-reflective coatings, etc., are applied onto microelectronic wafer substrates such as glass, silicon, etc., by a technique called spincoating. These coatings will invariably thicken and build up residues at the wafer's edge, often overflowing onto the backside of the wafer edge. These residues, often referred to as "edge beads", must be removed to avoid contamination during subsequent handling and processing.
If the "edge beads" are not removed prior to subsequent processing steps, such as softbake, exposure and development, then, during the course of such subsequent processing, the edge beads will tend to crumble, generating extraneous particles that lead to surface defects in the image topography.
Compositions to remove the "edge beads" are known as "edge bead removal solvents" or "EBRs".
In the past, "the" one active ingredient for all EBRs, known to be universally effective for composite microlithographic edge beads, despite the edge beads' particular polymer chemistry, is N-methylpyrrolidone (NMP). However, the EBRs containing NMP inherently require long spin cycles, after the cleaning application, to dry the edge of the substrate. Even then, such EBRs leave a further liquid residue which requires an additional baking step for removal. Also, the amine components in NMP can contaminate the photoresist.
When, in addition to removing a "photoresist" edge bead, it is also necessary to remove edge beads comprised of other layer material comprising highly polar aromatic polymers, further problems arise. Such polymers are characterized by having a predominance of benzenoid rings in the backbone of the polymer with the rings being connected by polar chemical linkages such as amic acid, sulfone, amide, urea, ether and carbonyl groupings. These polymers are formulated to avoid interfacial mixing with the photoresist and therefore have mutually exclusive dissolution characteristics from the photoresist and incompatible solvents. Typically, they also have glass transition temperatures (Tg) in excess of 100.degree. C.
Other EBR components, which might tend to solve the NMP problems, will not dissolve the highly polar aromatic edge beads, or tend to create dangerous peroxides, or are toxic, or will not rinse with water. Typical of such ineffective EBRs are ethylene and propylene glycol monomethyl ethers, the corresponding acetate derivatives, butyl acetate, ethyl lactate, ethyl-3 ethoxy-propionate, ethyl pyruvate, higher glycol ethers such as butyl Cellosolve.RTM., higher glycol ether acetates, glymes, notably diglyme; aliphatic, cycloaliphatic, aromatic ketones including cyclopentanone; aromatic hydrocarbons, tetrahydrofuran (THF) and alcohols.
Alcohols, including aliphatic (e.g., ethanol), cycloaliphatic (e.g., cyclohexanol) and aryl-aliphatic (e.g., benzyl alcohol) are generally known to be ineffective solvents for highly polar aromatic polymers.
An additional drawback to the employment NMP, or other chemically basic EBRs, is that they contaminate acid-catalyzed types of photoresist such as IBM's APEX.RTM. and OCG's CAMP IV.RTM. positive tone, deep ultraviolet acid-catalyzed photoresist. If the spin bowl is contaminated with basic impurities, such as amine material, then the photosensitivity of the resist is materially weakened, leading to defects in the image pattern. Absent thoroughly rinsing the spin bowl after each EBR spin, the accumulation of impurities serves to progressively deteriorate the integrity of each successive lamination.
In fact, in many instances, the amine contamination problems are so severe for acid-catalyzed photoresist, that manufacturers will avoid edge bead removal altogether, tending instead to cope with the particle defects that arise from the crumbling edge beads.
Other options for employing non-basic EBRs rather than NMP in the past have included the use of, for example, cyclohexanone. This method permitted softening and swelling of antireflective coatings edge beads and their partial removal. However, one serious drawback to such process is an attendant generation of a spider-web-like residue. Such residue requires a cumbersome and extraneous cleaning operation.
Accordingly, it is an object of the present invention to provide an improved microlithographic cleaning composition and method suitable for faster composite edge bead removal.
It is a further object of the present invention to provide an improved edge bead removal process for microlithographic edge beads including highly polar aromatic polymers without deleterious side-effects.
It is also an object of the present invention to provide an effective EBR composition for acid-catalyzed photoresist, negating interaction tending to contaminate the photoresist.
Another principle object of the present invention is to provide an improved method for edge bead removal with reduced spin cycle and which negates the need for a baking step when removing residual liquid EBRs.